This invention relates to glass laminates having enhanced resistance to penetration by high velocity projectiles. More particularly, the invention relates to relatively thin glass laminates which not only stop glass from spalling when impacted by small and medium caliber bullets but also stops penetration of the laminates by the bullets or other small high velocity projectiles.
Various types of transparent laminated structures have been disclosed for protecting personnel from flying splinters and fragments of glazing materials which are released when a high velocity projectile strikes the structure. In U.S. Pat. No. 3,658,636 thick plates of an amorphous polyamide are formed into a sandwich structure with silicate glass. U.S. Pat. No. 2,861,021 describes a structure in which polymethyl methacrylate sheets are laminated with polyvinyl butyral and faced with a layer of a polyamide, polyester or regenerated cellulose sheet. Multiple plies of glass and polyvinyl butyral are used in combination with a plastic interlayer as an impact absorption section in the structure disclosed in U.S. Pat. No. 4,130,684.
The problem of spalling of an anti-abrasion layer which is applied to a laminate using polycarbonate sheets is addressed in U.S. Pat. No. 4,812,359 by applying a thin polycarbonate sheet having an abrasion-resistant self-healing coating. A similar laminate which includes an internal elastic expansion core with a thin polycarbonate sheet covered with an antiabrasive which can be replaced is disclosed in U.S. Pat. No. 4,879,183. British Patent 828,381 discloses a five layer laminate consisting of two layers of glass, two layers of polyvinyl butyrate and a central layer of polyethylene terephthalate. Published UK Application 2 156 736A discloses an impact resistant laminate comprising a number of glass sheets which are laminated together with a rear polycarbonate sheet which is said to be resistant to spalling.
A problem with most "bullet resistant" structures is that they have a thickness in excess of that which can be accommodated in usual glazing applications. Some structures are effective in controlling spalling but are not effective in stopping penetration of the laminate by a projectile. Most of the structures rely on incorporating layers of various materials in the laminated structure. This complicates manufacture and increases costs since different materials require different laminating techniques.
It has been found that by permanently bonding a very thin composite consisting of an adhesive layer and a dimensionally stable polyester film to multiple plies of glass with layers of plasticized polyvinyl butyral there between, a glass laminate of substantially reduced thickness is provided which is capable of resisting penetration of high velocity projectiles with little, if any, spalling from the inner rear face of the laminate.